A scanning electron microscope (hereinafter abbreviated as an SEM) that is a type of charged corpuscular particle beam apparatus is an apparatus which accelerates primary electron beams emitted from an electron source, scans a spot beam focused on a specimen by using an electrostatic lens or a magnetic lens over the specimen in a two-dimensional manner, detects a secondary signal such as a secondary electron or a reflection electron generated as a secondary phenomenon from the specimen, and uses the intensity of the detected signal as an intensity-modulated input of a monitor scanned in synchronism with primary electron beam scanning, thereby obtaining a two-dimensional scan image (SEM image).
Along with recent miniaturization in semiconductor industries, SEMs have been used for semiconductor device manufacturing processes or inspection after completion of the processes (e.g., dimensional measurement by using an electron beam or inspection of electrical behavior) instead of optical microscopes. In observation of the multilayer thin film structure of a semiconductor device internal structure, efficient detection of not only a secondary electron having information on a specimen surface but also a reflection electron having inclination information allows surface shape measurement and defect detection evaluation. A modern SEM is provided with, e.g., an energy filter capable of separating secondary electrons and reflection electrons from each other and can form image contrast to suit the intended use. When an ArF resist or a Low-K material used in a recent semiconductor process is subjected to SEM observation, the ArF resist or Low-K material is found to suffer from shrinkage or deformation due to electron beam irradiation. Although this phenomenon can be alleviated by lowering accelerating voltage, the lowering reduces the resolution of an SEM and makes high-resolution observation difficult.
For this reason, a retarding method involving applying a negative voltage to a specimen, a boosting method intended to reduce primary electron beam chromatic aberration by arranging an accelerating electrode near an objective lens, and the like have been adopted to allow high-resolution observation even in a low accelerating voltage region. A detector using an orthogonal electromagnetic field generator for secondary signal separation (EXB) is used to efficiently detect secondary signals such as a secondary electron and a reflection electron emitted from a specimen. A typical example of such a detector is disclosed in Patent Literature 1.
Patent Literature 2 discloses a technique for forming a specimen image in desired contrast by constructing a detector using divided detection elements and performing signal processing according to the trajectory of an electron.